I have inherited from previous owner a rough shower stall in the basement in which he used a floor drain and built its walls using cement blocks, painting the whole thing including the still-exposed pipes with epoxy paint, very shiny. I want to redo the whole thing, furring out the walls and using cement backer-board, tiling it entirely. Question, since it was built on the basement concrete floor, should I still use a waterproof membrane for its floor? Any advice on furring out the cement block walls to ensure a permanent installation. Thanks for your help (and for this great informative system you have instigated here).